In vitro Assay of Transfer Factor (TF): We have described recently (Ascher et. al. PNAS 71:1178, 1974) a crude in vitro assay of TF whereby naive lymphocytes are converted to an antigen-responsive state following incubation with TF and then in the presence of the related antigen undergo transformation and proliferation with uptake of thymidine. We continue to perfect and explore this assay to adapt it for: 1) isolation and analysis of the active biochemical moiety in lymphocyte dialyzates; 2) detection of the precise donor cell and recipient cell engaged by TF; 3) attempt to elucidate the mechanism whereby an antigen-specific receptor site is conferred on naive lymphocytes. In vivo: TF Immunotherapy of Cancer: We continue studies on the effects of administration of melanoma-specific TF to patients with metastatic malignant melanoma as a tumor-model. In addition to evaluation of clinical and other in vivo effects studies are in progress to perfect a simple reliable in vitro assay of host cellular immunity to his tumor antigens to monitor the effects of TF administration.